1. Field of the Invention
The present invention involves a stable emulsion composition of water and a high boiling hydrocarbon distillate and vehicle and ink compositions containing the emulsion composition. A printing process is improved when it includes the emulsion composition.
2. Description of the Related Art
Industrial processes that involve the emission of volatile organic compounds (VOC) are being required by governmental regulations to reduce these emissions due to health and environmental concerns.
The printing industry uses volatile organic compounds generally as solvents in ink compositions. Printing methods that result in the emission of solvents, especially those in which solvent evaporation is used to dry the ink, can benefit from technology that reduces VOC emissions. Both letterpress and lithographic printing can employ evaporation of the solvent to dry an ink. Because letterpress printing is less convenient, more time consuming and more costly than lithographic printing in the preparation of printing plates for the printing press, lithographic printing has become the leading method for publication and commercial printing and an important method for printing packaging materials.
Lithographic printing is a complex process. The printing plate or plate cylinder for lithographic printing is a flat surface, not a raised or recessed surface. The plate cylinder contains an image area which is ink receptive. The image area can be generated by several methods to include a photographic process and a computer-to-plate process in which a sensitive coating on the plate is developed in the image area while in the nonimage area the coating is washed away leaving the nonimage area hydrophilic or water receptive. In a normal lithographic printing process the nonimage area on the plate cylinder is first wetted with an aqueous dampening solution rendering it nonreceptive to ink. Ink is then transferred to the image area on the plate cylinder. In direct lithographic printing the ink is transferred from the plate cylinder directly to the substrate being printed such as paper while in offset lithographic printing the ink is initially transferred to a rubber blanket cylinder and then to the substrate. Offset printing has advantages including that it provides an even image on an uneven substrate. Because of the complex process involved in lithographic printing, the ink must have certain properties on the printing press to include a certain tack or stickiness and viscosity or resistance to flow that allow transfer of the ink at the high speeds of a printing press and that result in an undamaged substrate having a image of proper intensity and definition.
DeSanto, Jr. et al. in U.S. Pat. No. 4,981,517 disclose a printing ink emulsion system containing an oil-based phase and water-miscible phase and exhibiting a high degree of stability against phase separation in use.
Koike et al. in U.S. Pat. No. 5,378,739 disclose a W/O emulsion ink for use in stencil printing which is composed of an oil phase and a water phase with the respective ratios by wt. % thereof being (20 to 40):(80 to 60).
Batlaw et al. in U.S. Pat. No. 5,389,130 disclose an ink composition for Gravure printing wherein the vehicle is a water-in-oil emulsion of a water immiscible organic phase and an aqueous phase in the range of 9:1 to 1:1 thereby significantly reducing VOC emissions with no detrimental effect on print quality.
Kingman et al. in U.S. Pat. No. 6,140,392 disclose single fluid lithographic printing inks that include a continuous phase and a discontinuous polyol phase.
Ohshima et al. in U.S. Pat. No. 6,348,519 disclose an emulsion ink, by which clear images are produced, having excellent drying and fixing properties and preservation stability and does not bleed, strike through or leak.
Unexpectedly it has now been found that an ink containing a water-in-oil emulsion, in which the water in the emulsion replaces organic solvent normally present in the ink, can be used in a lithographic printing process to produce a print equivalent in quality to print from a conventional lithographic ink. A lithographic process using an ink that contains this water-in-oil emulsion is improved in performance in several ways. Emissions of VOC can be reduced by an amount equal to the amount of organic solvent eliminated by using the emulsion. The evaporation step to dry the ink can result in a lower oven temperature since water generally boils at a lower temperature than the organic solvent which may also result in less energy being needed to dry the ink. A lithographic printing press run that uses an ink containing a water-in-oil emulsion meets print quality standards sooner compared to a run using a conventional lithographic ink which is advantageous timewise, energywise and in reducing substrate wastage.